fix cv::subtract function:

call dst.create(...) before using it(cherry picked from commit 4c66614e07)

modules/core/src/arithm.cpp

@@ -1562,8 +1562,12 @@ void cv::subtract( InputArray src1, InputArray src2, OutputArray dst,
         if (dtype == -1 && dst.fixedType())
             dtype = dst.depth();
 
-        if (!dst.fixedType() || dtype == dst.depth())
+        dtype = CV_MAKE_TYPE(CV_MAT_DEPTH(dtype), src1.channels());
+
+        if (!dst.fixedType() || dtype == dst.type())
         {
+            dst.create(src1.size(), dtype);
+
             if (dtype == CV_16S)
             {
                 Mat _dst = dst.getMat();

modules/core/test/test_arithm.cpp

@@ -1579,3 +1579,13 @@ TEST_P(Mul1, One)
 }
 
 INSTANTIATE_TEST_CASE_P(Arithm, Mul1, testing::Values(Size(2, 2), Size(1, 1)));
+
+TEST(Subtract8u8u16s, EmptyOutputMat)
+{
+    cv::Mat src1 = cv::Mat::zeros(16, 16, CV_8UC1);
+    cv::Mat src2 = cv::Mat::zeros(16, 16, CV_8UC1);
+    cv::Mat dst;
+    cv::subtract(src1, src2, dst, cv::noArray(), CV_16S);
+    ASSERT_FALSE(dst.empty());
+    ASSERT_EQ(0, cv::countNonZero(dst));
+}